Tiwari, Pravin KumarBehera, NarayanSingh, R. K.Joshi, H. C....
9页
查看更多>>摘要：A comparative study of laser induced breakdown spectroscopy (LIBS) of brass and aluminium targets has been performed under different experimental configurations, conditions i.e. in the presence of magnetic field and laterally colliding plasmas in the absence as well as in the presence of transverse magnetic field with an objective to improve the detection sensitivity of LIBS signal. Helmholtz coil with pulsed power system is used to generate transverse magnetic fields of 0.07 T and 0.21 T. Comparison of observed LIBS signals of single and colliding plasmas is presented. Significant enhancement in the intensities of observed LIBS lines is noticed in case of colliding plasma with magnetic field. LIBS analysis of the colliding plasma (interaction region) in the presence of magnetic field is attempted for the first time and observed results show drastic improvement in the detection sensitivity. Observed findings are correlated with the variation in characteristics plasma parameters in different experimental configurations. Calibration-free elemental analysis under different experimental conditions is also performed for comparative evaluation.
查看更多>>摘要：On-line detection of chlorine in cement is the key to evaluate the corrosion of the reinforced concrete inside the structure. A collinear dual-pulse LIBS system based on two nanosecond lasers with a total energy of 30 mJ is developed to detect the chlorine in cement. The key parameters of the dual-pulse LIBS system are optimized to improve the detection sensitivity of trace chlorine element in cement pastes, and the optimal values of the parameters are obtained to be: 4 L/min helium gas flow rate, 2000 ns inter-pulse delay, 800 ns gate delay, 19 mJ/11 mJ pulse energy ratio, and 42.8 mm lens-to-sample distance. After the optimization of the dual-pulse system, the signal-to-noise ratio of the trace chlorine emission line at 837.6 nm has been improved from 1.75 to 2.68 for a sample containing 0.706 wt% chlorine. The temperatures of plasma are obtained based on Saha-Boltzmann plot for exploring the plasma radiation features in the dual-pulse system. The results show that the plasma temperature which is influenced by laser irradiance and parameters of the double pulse configuration, is closely related to the signal-to-noise ratio of chlorine spectrum line. Sixteen standard cement pastes made from a series of sodium chloride solutions with various concentration are used for LIBS calibration. Two calibration methods including internal standardization and partial least squares regression are adopted for determining chlorine concentrations within a series of standard cement pastes, and the limit of detection based on internal standardization model is calculated to be 103.4 ppm. The prediction performance of IS and PLSR is evaluated by Leave-One-Out Cross-Validation with the root mean square error of calibration of 0.0910 and 0.0859, respectively.
查看更多>>摘要：Laser-induced breakdown spectroscopy (LIBS) is a versatile elemental analytical technique whose basic elements were described as early as 1962, shortly after the invention of a pulsed laser. Since that time, LIBS has been applied for elemental characterization of various applications. In this work, we review the evolution of LIBS characterization of artworks' materials applications and the development of the LIBS technique for cultural heritage during the years 2015-2020. The LIBS technique has faced and overcome challenges by analytical studies of conservation/restoration and archaeological objects. These challenges required improvements in the LIBS technology in order to obtain good reproducible signals (high S/N, sensitivity) and more reliable quantitative analysis. They also encouraged the LIBS research community to focus on instrumentation development to minimize laser impact, to increase miniaturization (enabling in situ characterization), and to combine different spectroscopic techniques. We aim to encourage more people working on heritage science to use this technique, for whom LIBS may be a brand-new elemental analysis technique, and aim to motivate more LIBS researchers to continue developing the LIBS technique in order to address more issues on conservation, restoration, and archaeology.
查看更多>>摘要：The accuracy of laser-induced breakdown spectroscopy (LIBS) methods for analyzing geological samples is improved when calibration standards and unknown targets are compositionally similar. A recent study suggests that customized submodels can be used to optimize calibration datasets to achieve more accurate predictions [1]. In practice, this is difficult to implement because the errors inherent in the methods used for sorting unknown targets by composition may affect how successfully this matching can occur. Moreover, creation of submodels intrinsically reduces the size of the dataset on which the model is trained, which has been shown to reduce prediction accuracy. This paper uses LIBS spectra of 2990 unique rock powder standards to compare the accuracy of 1) submodels generated for each element over its geochemical range, 2) submodels created using SiO2 content only, 3) submodels created using the ratio of Si(II)/Si(I) emission lines to group spectra by a proxy for approximate plasma temperature, and 4) models created using all data. Results indicate that prediction accuracies are not always improved by creating submodels because subdividing a dataset to optimize calibrations will always result in a smaller database available for each submodel, and the reduced training set size negatively affects accuracy. Customized LIBS standards for specific applications might overcome this problem in cases where the matrix is similar and the expected concentration range is known. But in a majority of geochemical applications, submodel approaches are only useful in improving prediction accuracies when the initial database is itself extensive enough to support large, robust submodel calibration suites.
Patil, Ajay B.Tarik, MohamedSchuler, Albert J.Torrent, Laura...
11页
查看更多>>摘要：The advent of rare earth elements (REEs) with optoelectronic properties has shifted the technology paradigm from digital to a smart and hybrid world. Their substantial uses also resulted in a large piling up of e-waste. Therefore, e-waste is now a lucrative recycling target for the recovery of such critical raw materials. Their recycling from e-waste is often challenged by dilute metal concentration, complex composition, and difficult chemical characterisation. Generally, the characterisation of e-waste involves elemental determination techniques, such as inductively coupled plasma optical emission spectroscopy (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS). ICP-OES is attractive for a recycling or research sector because it has a higher matrix tolerance and lower cost than ICP-MS. In this work, the intensity at 445 line positions measured by an ICP-OES instrument was compiled in a 2D diagram to map interferences by 27 prominent lines from 9 REEs. The second diagram shows the impact at 230 neighbouring line positions measured in each of, in total, 17 (i.e., 9 REEs and 8 non-REEs) single-standard solutions in terms of the concentration of the element type affected. The spectral interference correction algorithm proposed here had been developed by us for a recycling process to obtain pure Y, Eu, and Tb from fluorescent powder (FP) in spent lamps. The ICP-OES analysis and spectral interference correction approach presented here can be applied to any element and e-waste type. To underline this, the paper gives examples for elements in dissolved FP and surrogate NdFeB magnet samples.
查看更多>>摘要：Natural carbonate standards of calcite structure were analysed using a handheld Laser-Induced Breakdown Spectroscopy (LIBS) device to investigate the spectral applicability for quantitative analysis in the Ca-Mg-Fe-Mn carbonate system. To obtain an initial understanding of the relationship between the elemental concentrations and LIBS signals, the determination coefficient (R-2), root mean square error (RMSE) and mean arctangent absolute percentage error (MAAPE) for cross-validation and forecast accuracy were used, respectively. To relate the changes in spectral characteristics to the mineral content of carbonate mixtures, different spectral ratios were compared with mixture ratios between the two carbonate minerals. We found that spectral information from LIBS emission lines showed high correlations to their elemental concentration (Ca, Mg, Fe, and Mn), and their spectral ratios in carbonate mixtures showed a linear correlation with mineral content. Principal component analysis (PCA) was investigated the chemometric capability of the discrimination for carbonate minerals. This study demonstrates that handheld LIBS can be effectively applied in the field for the discrimination and identification of carbonate endmembers and their quantification for the case of mixtures.
VanBommel, S. J.Gellert, R.Berger, J. A.McCraig, M. A....
7页
查看更多>>摘要：Geochemical analyses by X-ray spectrometry and laser-induced breakdown spectroscopy (LIBS) instruments on the surface of Mars enable detailed studies of surface materials. The two techniques are utilized in concert by rovers to glean information in a complementary fashion. However, fundamental differences in how these analytical techniques function can produce perceived discrepancies in results, such as those resulting from variation in sampling volume. Here we utilize data acquired by the APXS (X-ray spectrometer) and ChemCam (LIBS) instruments on the Curiosity rover to investigate a manganese-rich surface layer, and, in the process, provide an improved chemical depth profile. We also demonstrate a method whereby current and future spacecraft capable of utilizing both techniques can potentially improve estimates of martian material nearsurface density.
查看更多>>摘要：Quantitative analysis methods in all applications require robust measurements of quantification limits (LOQ); the threshold at which predicted values can be trusted. Although established LOQ protocols exist for univariate techniques, based on classical peak area measurements that vary directly with concentration of analytes, there is limited work on how best to quantify measurement limits when analyzed using more modern multivariate analysis (MVA) methods. This is especially the case for the technique of laser-induced breakdown spectroscopy (LIBS), which in the last decade has emerged as a promising technique for elemental analyses in many LIBS applications, wherein MVA modelling techniques outperform univariate methods. Accordingly, this study provides the final step in a protocol for generating robust quantification models for LIBS, with carefully determined accuracies for geological applications within. Its goal is to provide a template for calculating LOQ based on multivariate LIBS regression models, and to understand how this value is affected by several external factors: instrumentation (Mount Holyoke College ChemLIBS vs. Los Alamos National Laboratory ChemCam flight model), outlier removal method (highest natural concentration vs. statistically-based method), and acquisition atmosphere (Mars vs. air vs. vacuum), for two methods of calculating instrument sensitivity from experimental data (taken from metal spectra vs. noise-free regions of rock spectra). Partial-least squares regression models are made for almost every combination of the aforementioned parameters for the major oxides MnO, Na2O, SiO2 and minor and trace elements Li, Ni, Pb, Rb, Sr, and Zn. ChemLIBS models use 2607 geochemical standards, while ChemCam and ChemLIBS comparison models use 205 standards common to both instrument's datasets. Because LOQs determine the minimum predicted concentration to have confidence in, these values have a direct impact on model testing errors. The effect of LOQ on model validation is also summarized by comparing test accuracies before and after LOQ application. This step is essential to fully understand appropriate quantification of rock geochemistries with LIBS. Results show that LOQ is influenced by the variety within the composition of training standards and penalizes regression vectors that over- or under-fit the calibration data. These characteristics make LOQ an essential metric for better understanding model quality `behind the scenes', in addition to common measures like test accuracy and R-2 correlation. Applying LOQ to MVA models is therefore especially important when quantifying elements within such complex standards as rocks.
查看更多>>摘要：The trace carbon (C) composition in ultra-low carbon steel is measured by Laser-Induced Breakdown Spectroscopy (LIBS). Five standard steel samples, with C content between 9 and 89 mu g/g, are used to study the performance of LIBS quantitative analysis. Single-pulse LIBS (SP-LIBS) and long-short double-pulse LIBS (LS-DP-LIBS) have been used to measure these five samples. Due to the carbon contamination on sample surface, SP-LIBS cannot obtain an available analysis result. To reduce the influence of carbon contamination, the pretreatment pulse method is employed in this work. The experimental results of the continuous irradiation show that the long-short pretreatment pulses can effectively eliminate the influence of carbon contamination. Finally, the trace carbon in steel samples has been successfully measured by LS-DP-LIBS with pretreatment pulses. The LOD value of carbon is 22.6 mu g/g. For the measured five samples, the relative error of prediction (REP%) is between 6.1% and 35.7% and the relative standard deviation (RSD%) is between 13.9% and 58.3%.
查看更多>>摘要：Fast measurement of caking index (G) and maximum thickness of plastic layer (Y) of coal is urgently needed for process optimization in coking industry to improve coke quality and reduce CO2 and pollution emission. Till now, there has not been any report on fast determination of these two coal property parameters yet. In the present work, laser-induced breakdown spectroscopy (LIBS) was utilized for the fast measurement of G and Y value as the first time. A dominant factor based partial least square (PLS) model combined with variable selection was applied to improve measurement performance using 189 coal samples. Thirteen important lines which physically correlate with G and Y were chosen in establishing the dominant factor model, and the residual errors were further corrected by PLS together with variable selection to avoid noise overfitting. The proposed model showed satisfactory quantitative measurement of G and Y, which were very close to the Chinese national standard based on traditional laboratory method. Compared with the traditional PLS model, the root mean square error of prediction (RMSEP) for G value was reduced from 5.117 to 4.197, with an improvement of 17.9% relatively. The RMSEP for Y value was reduced from 1.588 to 1.036, with an improvement of 34.7% relatively. The improvement brought by the dominant factor model and the variable selection method was discussed in detail. Results showed that LIBS is capable of fast measurement of the values of G and Y of coal for coke industry.
NSTL
Elsevier